The purpose of this work is to examine the physical chemistry of the gelation of sickle cell hemoglobin and, through understanding of the processes of gelation, to inhibit or minimize this deoxygenation dependent phenomenon which produces the pathophysiological events in sickle cell disease. The principle direction of the current work is to define and characterize the different transitions, phases and phase changes which occur in gelation. At present sequential ultracentrifugal assays on a single sample have served to define the onset of measurable amounts of aggregation of monomers into polymers, measured by a monomer concentration Cagg, as distinguished from the separation of the gel into two conjugate phases, measured by another monomer concentration, C sat. This method permits approaches to the thermodynamic properties of two separate equilibria, polymerization characterized by C agg, and the entropically governed phase separation into isotropic and anistropic portions characterized by C sat. Specific conclusions and work in progress concern factors which govern the existence of various macroscopic phases and which might divert condensation from one such phase to another, identification of the phase or phases which are most pathogenic, and aspects of the nature and equilibria of intermediates in the overall transition from monomers to gel.